INTEGRAL gives itself more time
14 June 2001ESA's International Gamma-Ray Astrophysics Laboratory INTEGRAL is giving itself more time to be ready for launch. Lift-off on a Russian Proton launcher was previously envisaged in April 2002.
A recent mission status review has concluded that the launch should be rescheduled. The new launch date, 7 October 2001, has been discussed with the Russian partners which are contributing to the INTEGRAL mission with a Proton launcher. Actions are taken from their side to modify the launcher planning for this period. This new launch date will also allow the maximum possible manufacturing and calibration time for one of the observatory's main science instruments which has encountered some production difficulties.
INTEGRAL, an ESA mission in co-operation with Russia, will gather the most energetic radiation that comes from space. With its gamma-ray spectrometer (SPI) and gamma-ray imager (IBIS), it will be the most sensitive gamma-ray observatory ever to be launched. The payload also includes two X-ray monitors (JEM-X) and an optical camera (OMC) to help identify gamma-ray sources.
Production of part of the IBIS camera involves the delicate bonding together of some 4000 small elements. These crystals and photodiodes constitute the lower detector layer of the instrument called 'PICsIT' (PIXellated Caesium Iodide Telescope). Despite stringent controls that had preceded their large-scale manufacture, some units have subsequently been seen to degrade during environmental tests, which recreate the harsh conditions of space.
Under the direction of the IBIS Investigators, an alternative technology using so-called 'soft silicon glue', which has already been used in space, has now been validated. Initial tests on a batch of PICsIT detectors have indicated the very good optical and thermal performance of this bonding. Procurement has been launched and after final qualification, production of the new detectors is about to start.
Commenting the decision, ESA's Director of Science, David Southwood, said: " I am very relieved that after considerable efforts, the IBIS team has found a reliable solution. With its powerful capabilities of fine imagining and spectral sensitivity, IBIS is fundamental to the success of the INTEGRAL. Every space mission, with science instruments that are so sensitive and complex, encounters such difficulties, and when they do arise it is always better to be safe than sorry."
Assembly of the INTEGRAL spacecraft is proceeding normally at the Alenia Spazio Turin facilities. The OMC camera, delivered last October, has been installed. The SPI spectrograph has undergone calibration tests and is now integrated onto the spacecraft where its undergoimg system tests. The JEM-X cameras are also approaching delivery, as is the second upper component of the IBIS imager, ISGRI (Integral Soft Gamma-Ray Imager).